1. Field of the Invention
The present invention relates to an auto-accompaniment apparatus for, e.g., an electronic musical instrument.
2. Description of the Related Art
In an auto-accompaniment apparatus in a known electronic musical instrument, chord type data (major, minor, seventh, or the like, and chord root data (C, D, E, . . .) are detected from information of a key depression operation, and chord data (chord tone data) necessary for an accompaniment operation are generated on the basis of the above data with referring to prestored accompaniment pattern data (formed with reference to, e.g., C major).
Accompaniment pattern data consists of a string of note data constituting a chord, and each note data consists of several bytes indicating a tone pitch (key number), a tone generation timing, a tone generation duration, a tone volume, and the like. The accompaniment pattern data are prepared in units of types of rhythms, and are repetitively read out from a ROM at a tempo designated in correspondence with a selected rhythm.
The ROM stores tone pitch difference values (offsets) in units of chord types (major, minor, and seventh) with respect to reference chords belonging to, e.g., C major in the form of a look-up table.
Chord type data and chord root data are detected from key operation information input by a player. The tone pitch difference value corresponding to the detected chord type data is read out from the ROM. The difference value and a root value are added to key scale numbers representing notes programmed as the accompaniment pattern to be read out from the ROM, thereby obtaining key number data of chord tones to be generated. A tone source unit generates accompaniment tones on the basis of the modified key numbers, and tone generation duration data and tone volume data of chord notes read out from the ROM.
The conventional auto-accompaniment apparatus has only one development method which uses a look-up table for development from reference chords to chord tones corresponding to chord types instructed by a player. For this reason, when chords are changed, the tone pitches of accompaniment tones abruptly leap, resulting in an unnatural play.
For example, when a chord is changed from C7 to G7, notes (C, E, G, Bb) are abruptly changed to (G, B, D, F), i.e., all the tones abruptly become higher by perfect fifth.